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Date:      Mon, 12 Oct 2015 22:47:38 -0400 (EDT)
From:      Rick Macklem <rmacklem@uoguelph.ca>
To:        Christian Kratzer <ck@cksoft.de>
Cc:        freebsd-stable@freebsd.org, John Baldwin <jhb@freebsd.org>
Subject:   Re: smbfs crashes since approx. 10.1-RELEASE
Message-ID:  <173739656.33429352.1444704458926.JavaMail.zimbra@uoguelph.ca>
In-Reply-To: <alpine.BSF.2.20.1510121552090.47677@noc1.cksoft.de>
References:  <alpine.BSF.2.20.1510051157450.16263@noc1.cksoft.de> <3563189.eDHDcCgW5L@ralph.baldwin.cx> <alpine.BSF.2.20.1510091107010.71292@noc1.cksoft.de> <358885214.31305796.1444518367048.JavaMail.zimbra@uoguelph.ca> <alpine.BSF.2.20.1510120946150.47677@noc1.cksoft.de> <alpine.BSF.2.20.1510121008010.47677@noc1.cksoft.de> <2135054744.32546564.1444653156980.JavaMail.zimbra@uoguelph.ca> <alpine.BSF.2.20.1510121552090.47677@noc1.cksoft.de>

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Christian Kratzer wrote:
> Hi Rick,
> 
> On Mon, 12 Oct 2015, Rick Macklem wrote:
> 
> > Christian Kratzer wrote:
> >> Hi Rick,
> >>
> >> there was also a second more recent crash in /var/crash
> >>
> >>      Mon Oct 12 03:01:16 CEST 2015
> >>
> >>      FreeBSD noc3.cksoft.de 10.2-STABLE FreeBSD 10.2-STABLE #2 r288980M:
> >>      Sun
> >>      Oct 11 08:37:40 CEST 2015
> >>      ck@noc3.cksoft.de:/usr/obj/usr/src/sys/NOC  amd64
> >>
> >>      panic: Assertion mtx_unowned(m) failed at
> >>      /usr/src/sys/kern/kern_mutex.c:955
> >>
> > Oops, I screwed up. I should have looked at this panic assertion when you
> > reported
> > it before. Ok, so if I understand the assertion correctly, it means that
> > another
> > thread has the mutex locked. If this is correct, I'll have to take another
> > look at
> > the code and figure out how to wait for these other threads to finish with
> > the mutexes.
> >
> > I do think the patch fixes the race I saw, but there must be other races in
> > the code.
> >
> > I'll take another look, but if anyone else is conversant with netsmb, feel
> > free to
> > jump in, because it is all new to me.
> >
> > Unfortunately, I won't have any way to do testing for the next month or so,
> > so any
> > patches I do come up with will be "try this untested..".
> 
> thats no problem.
> 
> Just keep the patches coming when you have time and tell me when to reset
> back to stable,
> current or whatever so we don't lose sync of the status.
> 
Well, you can try the attached one instead of the previous ones (ie. against stable).
It just delays destroying the mutexes until the iod thread is exiting.

I can't quite see why the previous patches wouldn't fix it, but this one leaves
smb_iod_main() unchanged, so it is a simpler patch and doesn't affect semantics
except for a slight delay in destroying the mutexes.

> As it looks like that the race happens on unmount I could try putting a sleep
> 60 into the
> script that does the "mount && rsycn && umount" magic just before the umount.
> That would
> allow anything that it slow to go away to perhaps release the mutexes before
> the umount.
> 
If it still crashes with this patch, it might be worth a try.

Or, if this patch still crashes, you could just delete the 3 lines that the
patch moves, so the mutexes are never destroyed. This would result in a leak,
but it would tell us if destroying these mutexes is the problem.

Thanks for your willingness to test these, rick

> Not a real fix of course but might help to verify what's going on.
> 
> Greetings
> Christian
> 
> 
> --
> Christian Kratzer                   CK Software GmbH
> Email:   ck@cksoft.de               Wildberger Weg 24/2
> Phone:   +49 7032 893 997 - 0       D-71126 Gaeufelden
> Fax:     +49 7032 893 997 - 9       HRB 245288, Amtsgericht Stuttgart
> Mobile:  +49 171 1947 843           Geschaeftsfuehrer: Christian Kratzer
> Web:     http://www.cksoft.de/
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> 

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